In the field of computer systems, digital data is often written onto magnetic media, which retains the data so that it can later be retrieved. One such mass storage mechanism is known as a hard disk drive. Commonly, hard disk drives are comprised of a stack of circular disks mounted on a spindle. A motor rotates the disks about the spindle. A number of transducers, more commonly referred to as "heads," are used to both read digital data from and write digital data to the magnetic media coating the disks.
A servomechanism is used to locate the heads in reference to radial locations over the disk surface. The servomechanism instructs an actuator to reposition the heads from one radial location to the desired radial location. As the heads are moved radially across the spinning disks, a number of concentric rings are described. These concentric rings, containing the digital bits of data, are known as "tracks."
Typically, a head is housed in a slider. Sliders are designed to be lifted by the air flow produced by the rotating disks so that they "fly" over the surfaces of the magnetic disks. The goal of disk drive designers is to maintain the sliders at an optimum flying height in order to minimize read and write errors. This can be rather difficult, due to imperfections inherent in many disks. Disks can have variations in their thickness both along particular tracks and from their interior to their exterior.
In order to compensate for the uneven height variations found in many disks, flexures (also known as gimbal springs and suspensions) are often implemented. A slider is mounted at the tip of a flexure. The other end of the flexure is attached to the actuator. Flexures have the degree of flexibility necessary to pitch and roll with imperfections found in the disks. This is typically accomplished by implementing a dimple on the surface of the flexure. The dimple is a small, dome-shaped protrusion. The dimple's apex provides a contact point about which the slider can pitch and roll to accommodate variations in the topography of the disk.
However, there is a problem encountered with this type of head assembly during seek operations. When a computer directs the disk drive to position the head .on a track different from the track wherein the head is presently positioned, the disk drive performs a "seek". The time required to perform a seek is a measurement of the level of performance of a disk drive. Fast seek times are prized because it translates into less time required to read and write the data, reducing the user's delay time. Hence, the heads are rapidly accelerated and then decelerated to quickly reposition the heads in an effort to minimize the seek time. This produces large acceleration and deceleration forces on the head assembly. The head is subjected to upwards of 200 Gs of acceleration. As a result, a seek can cause the slider to slip in a radial direction relative to the dimple. Friction can cause the slider to stick in that position, even after the seek has been completed. This undesirable phenomenon is known as the slip/stick problem.
The problem is that slip/stick occurrences can cause the slider to be off center to such a degree that the head is in an off track position. The effect is that although the actuator is moved to its correct location, the slider and the head are misaligned. This could cause track misregistration, resulting in read and write errors. Moreover, this problem is compounded by the fact that when the actuator is moved in one radial direction, the slider might slip and stick in that direction; yet if the actuator is subsequently moved in the opposite radial direction, the slider might slip and stick in the opposite radial direction. Further complicating matters is the possibility that the slider might slip and stick in one radial direction during a write operation, whereas it might Slip and stick in the opposite radial direction when attempting to read the written data. Given that the width of a track may be less than 500 minches, small displacements due to the slip/stick problem can cause an otherwise proper seek to fail.
Both linear and rotary actuators suffer from-slip/stick problems. Whereas linear actuators move the heads-along a straight radial line from the center of the disk, rotary actuators pivot about a point to swing the heads into position. Because rotary actuators typically have lower inertia in comparison to linear actuators, they can be moved and stopped more quickly, resulting in faster access times. However, the fast speed of rotary actuators produces larger acceleration and deceleration forces in the process of seeking a particular track. Hence, slip/stick problems are even more acute in disk drives having rotary type actuators.
One solution to the slip/stick problem is to increase the width of each track to provide greater tolerances for the placement of the heads. However, wide tracks occupy more room. Consequently, less data can be stored within a given disk area if wider tracks were implemented. In other words, this solution reduces the capacity of a disk for storing data.
Another proposed solution involves applying lubricant to the dimple area. However, this approach is typically unreliable due to inconsistent control of the lubricant characteristics. In addition, the lubricant might make the dimple more susceptible to corrosion.
Yet another prior art solution involves mounting the flexure at a ninety degree rotation to increase the flexure's lateral stiffness. However, this prior art solution could detrimentally impact the flexure's longitudinal characteristics. Furthermore, it typically requires additional hardware modifications.
Thus, what is needed is a mechanism for minimizing the effects of potential slip/stick occurrences while minimizing detrimental side effects. It would also be highly preferable if existing disk drive head assembly designs are not required to be modified.